Why Metric prefixes just move the decimal point: kilo means one thousand, so 1 kHz = 1,000 Hz. Dividing 1,500,000 Hz by 1,000 gives 1500 kHz, which is the same as 1.5 MHz since mega means one million.
Watch out 1500 MHz sounds similar but means 1,500,000,000 Hz, a thousand times too big; 150 kHz is only 150,000 Hz, ten times too small.
Hz to kHz, drop 3 zeros; kHz to MHz, drop 3 more. 1,500,000 Hz = 1500 kHz = 1.5 MHz.